Refining lead



' N l T E T A T E 1111 Patented Feb.- 23, i926.

HENRY HARRIS, OF LONDON, ENGLAND.

REFINING LEAD.

No Drawing. Application filed July 8, 1924, Serial No. 724,899. Renewed October 2Q, 1925.

Without the loss of any substantial amount of lead by permanent oxidation thereof. More particularly, the invention has for its object the separation of arsenic, tin and an- .timony from the lead'and lead alloys by means of. alkali hydroxid in the presence of an oxidizer, in such manner that at the end of the reaction the alkali melt is substantially free from lead oxide and contains substantially the oxides of the impurities to be removed, that is, the oxides of arsenic, tin and antimony. Preferably solid oxidizer, such as sodium nitrate is used. Suitable manufactured gaseous oxidizers are not exeluded, but I recommend the use of solid oxidizers inpractice. Owing to the freedom of the resulting alkali melt from any substantial lead oxide as obtained by this invention, the invention results in the great economical advantage that there is substantially no loss of lead in the refiningprocess This application is in the main 2. continuation of my copending application Serial No. 568,632, filed June 15, 1922, for improveinents inrefining lead.

I have found that if molten lead while being treated with a molten alkali hydroxid is maintained at low temperature, not exly oxidize the above-mentioned impurities (or suclrof them as are present) with no substantial loss of lead by permanent'oxidation, i. e., no appreciable amount of leadoxide or alkali oxysalt of lead will be found in the resulting alkali melt.

I have found that in'using oxidizers, preferably 'solid oxidizers with an alkali hydroxid for the refining of lead, that an alkali melt free from lead oxide and/or lead oxysalt, may be obtained if, in carrying on the reaction between the alkali hydroxid and.

the molten lead, the lead is maintained at a proper low temperature and the quantity and rate of addition of the added oxidizer is controlled'according to its efficiency as an oxidizer, so as to prevent'the formation of an excess of lead oxide, that is to say of more lead oxide than the, impuritiespresent in the lead can decompose at the time. It is probable, according to observations made in carrying out the process, that the oxidation of the impurities to be separated from the lead, takes place by the intermediate formation of lead oxide and/or sodium plumbate or sodium plumbite, in such a Way that a quantity of lead oxide, corresponding to the quantity of the oxidizer or oxidizers present at any time, is constantly formed by the oxidizer. The lead oxide or oxysalt then acts on the arsenic,'tin or antimony present in the lead, and is converted into metallic lead. According to the present invention, this intermediate formation of lead oxide should, however, be so regulated by the correct measurement of the quantity of oxidizer that all the lead oxide formed may be reconverted sufiiciently rapidly and completely into metallic lead by the impurities present in the lead. This is preferably accomplished by adding oxidizer at such a speed that this carrier (the compound of lead; oxide and sodium) is not produced in quantities much in excess of the quantity which can be decomposed at any one time by the impurities in the lead with which it comes into contact, so that at no time is there a substantial surplus of oxidizer or of lead oxides or oxysalts' in the alkali melt.

It is probable that in the ordinary lead softening or improving process, air is ca, pable at suitable temperature, of oxidizing zinc, arsenic, tin, antimony, and other easily oxidized metals, preferentially to lead; in practice, however, the process was only successful if a large proportionof the leadis simultaneously oxidized.

'Alkali nitrate has been proposed as an oxidizer of these metals, but it has been used in such quantities, under'such conditions, and with the lead at such high temperatures that its action was such as to cause permanentoxidation of lead simultaneously with the oxidation of the impurities towards which it therefore exerted, for practical purposes,,no preferential action. The condi .tions foravoiding the simultaneous oxideabout 500 C.,-and pass it in divided or sprayed form into a suitable molten alkali hydroxid reagent, preferably sodium hydroxid, and preferably having added there- .to sodium chlorid, and I utilize partially or entirely as the oxidizing agency, suitable solid oxidizers, such for example as sodium nitrate or others hereinafter mentioned, gradually added to the molten reagent in such relatively small quantity and while maintaining the lead at such low temperature that at no time is there a substantial surplus of oxidizer or of lead oxides or oxysalts in the alkali melt. Many materials may be used as oxidizers, especially such as alkali nitrates, nitrites and chlorates, which can be used at said low temperatures of the lead for preferentially oxidizing these impurities in lead with no appreciable loss of lead by oxidation.

Among-suitable oxidizing agents capable of being used in the above setforth manner, i. e., when the lead is treated by a molten-caustic alkali reagent, are solids such as alkali nitrate or nitrite, alkali chlorate or hypochlorite or other salt or a peroxide, adapted to part readily with oxygen at a temperature of between the melting point of lead and about 500 C. i

I have found a mixture of fused caustic soda, preferably mixed with sodium chlorid, and added sodium nitrate added gradually, a very suitable reagent for my purpose of course, the corresponding potassium compounds are equivalent in action, excepting that when potassium salts are used, the subsequent working up and treatment of the fused residue or melt becomes more difiicult than when sodium salts are used.

I have also ascertained that a mixture of fused caustic alkali with alkali chlorate with or without alkali chlorid or other fusible chlorid is an efficient reagent.

The proportion of oxidizing agent used and the temperature of the application may be so graduated as to permit to some extent, where so desired, of the progressive removal of some of the impurities in turn, without any appreciable loss of lead in form of oxide.

- The operation is preferably conducted by circulating the molten metal through the molten caustic alkali or mixture of alkali and'chlorid contained in a vertical cylinder out the operation, introduced gradually into the cylinder containing the molten reagent, by any convenient means such as an automatic feeder (for example that described and claimed in my co-pending application Serial No. 605,597, filedDecember 8, 1922),

regulated to pass a given quantity in the desired time. For the best results it is very desirable to feed the oxidizer gradually to the molten reagent as the molten lead is being passed through the molten reagent, since it has been found thateven Where a given relatively smallquantity of the oxidizer is used in the molten reagent, that if it is fed to the reagent too fast at any stage of the operation both the reagent and oxidized lose in efiiciency and lead in an oxidized form will pass permanently into the reagent.

The amount of added oxidizer relative to the amount of lead to be treated varies, of course, with thepercentage of impurities in the lead to be treated. If in the treatment of a given amount of lead containing a certain percentage of impurities only a certain percentage by weight of the oxidizer can be used without resulting in permanently oxidizing the lead, then in the treatment of the same amount of lead with a greater percentage of impurities, a proportionately greater percentage of the oxidizer can be used without permanently oxidizing the lead.

For instance it is found that in practice a quantity of sodium nitrate equivalent in weight to about 100 per cent of the arsenic, 61 per cent of the tin and 59 per cent of the antimony contained in lead is just sufficient completely to oxidizethese impurities. The rate of addition will depend upon the rate at which the impure lead is circulated through the reagent that is to say, the rate at which impure surfaces of the stream of lead are brought into contact with the oxysalt of lead produced through bringing together oxdizer," lead and molten reagent, also the rate at which the impurity can decompose the oxysaltof lead.

If in the case of an impure lead containing arsenic, tin and antimony, only suflicient nitrate of soda is gradually added equivalent in weight to 100 percent of the arsenic present, then substantially only arsenic will be removed.- If the lead from which the arsenic has been removed be then circulated through a fresh quantity of molten reagent to which-there is gradually added a quantity of sodium nitrate equivalent in weight to 61 per cent of the tin present, the resultant reagent will be found to contain for the most part the tin and only a little antimony. Similarly for the removal of the antimony the impure metal can be circulated through a fresh'portion of molten reagent gradually adding sodium nitrate equivalent in weight to 59 per cent of the antimony present when it will be found that all the antimony has been removed. If after this, further quantities of sodium nitrate .are added, the reagent will turn yellow and will contain oxide v of lead or alkali oxysalt of lead.

nently oxidized until all the said impurities have been completely removed.

The following examples illustrate the invention:

Example 1.50 short tons of a crude argentiferous lead containing 0.25 per cent of antimony are melted and passed through a molten mixture of caustic soda (72 per cent strength) 850 lbs., sodium chlorid (95 per cent strength) 600 lbs., into which sodium nitrate (95 per cent strength) 200 lbs. is gradually introduced over a period of about 6 hours. The temperature of the molten metal is about 420 C.

The antimony passes into the molten reagent and for the most part is left in an insoluble oxidized form, when the latter is dissolved in water, so that it can be separated from the solution, which may then be evaporated and again used with more OX1- dizing agent. Practically none of the lead passes into the reagent and the yield of refined lead may be expected to be one hundred percent. 7

Example 2.50 short tons of a crude argentiferous lead containing 0.25% of antimony are melted and circulated through a molten mixture of caustic soda (98% NaOH) 375 lbs., sodium chloride (95% strength) 88 lbs., into which sodium nitrate (98% strength) 148 lbs. is gradually introduced over a period of about 3 hours. The temperature of the molten metal is about from the solution, which may then be evaporated and again used with more oxidizing agent. Practically none of the lead passes into the reagent and the yield of refined lead may be expected to be one hundred per cent.

Example 3.50 short tons of a crude argentiferous lead containing 0.134 per cent of tin, 0.103 per cent of arsenic, and 0.287 per cent of antimony, are treated in a similar manner with a molten mixture of caustic soda (72 per cent strength) 1300 lbs., sodium chlorid (95 per cent strength) 950 lbs. to which sodium nitrate 340 lbs. is gradually introduced. The temperature of the molten metal is regulated at between 400420 C.

The tin, arsenic and antimony pass into the reagent. When this latter is' dissolved in water, substantially all the antimony is left in an insoluble oxidized form. Thetin and arsenic are found in the solution from which they may be individually separated.

Practically none of the lead is retained by the reagent, and the yield of refined lead may be expected to be 100 per cent.

Example 4 -50 short tons of a crude argentiferous lead containing 0.1% of arsenic, 0.1% of tin and 0.3% of antimony, are treated in a similar manner with a molten mixture of caustic soda (98% NaOH) 1080 lbs., sodium chlorid (95% strength) 288 lbs., to which sodium nitrate (98% strength) 33'? lbs. is gradually introduced. The temperature of the molten metal is regulated at between 400 and 420 C.

The arsenic. tin and antimony pass into the reagent. When this latter is dissolved in water, most of the antimony is left in an insoluble oxidized form. The arsenic and tin are found in the solution from which they may be individually separated.

Example 5.-50 short tons of a crude argentiferous lead containing 0.134 per cent of tin, 0.103 per cent of arsenic and 0.287 percent of antimony are passed into a. molten mixture containing (a) caustic soda (72 per cent strength) 370 lbs., sodium chlorid (95 per-cent strength) 250 lbs., to which sodium nitrate lbs. is similarly added.

Ninety per cent of the arsenic is extracted from the lead and passes into the reagent in an oxidized form unmixed with either tin or antimony which remain with the lead, practically none of which is oxidized. The temperature of the molten metal is 400 C. The arsenic may be recovered from the solution of the reagent.

(b) The lead now freed from most of its arsenic is passed into a fresh molten mixture consisting of caustic soda (72 per cent strength) 275 lbs., sodium chlorid per cent strength) 190 lbs., to which sodium nitrate 68 lbs. are gradually added.

The remainder of the arsenic and nearly all of the tin is extracted and passes unmixed with lead oxide into the reagent, from which it may be recovered.

The temperature of the molten metal is 400 C.

- passing it into a further quantity mixture of caustic soda (0) The lead now contains no arsenic, and 1s practically free from tin. It is finally treated'for the removal of antimony by passing it into a further quantity of molten recovered by evaporation. The lead is now in a particularly pure refined form. The yield will be practically 100 per cent of the original contents.

Example 6'.50 short tons of a crude argentiferous lead containing 0.1% of arsenic, 0.1% of tin and 0.3% of antimony are circulated through a molten mixture containing caustic soda- (98% NaOH) 262 lbs., sodium chloride (95% strength) 7 4 lbs., to which. sodium nitrate (98% strength) 90 lbs. is similarly "added.

Ninetyper cent of the arsenic is extracted from the lead and passes into the reagent in an oxidized form unmixed with either tin or antimony which remain with the lead, practically none of which is oxidized.

The arsenic may be recovered from the solution of the reagent. employed is about 400 to 420 C.

(2')) The lead now freed from most of its arsenic is circulated through'a fresh molten mixture consisting of caustic soda (98% NaOH) 354; lbs., sodium chloride (95% strength) 10d lbs. to which sodium nitrate (98% strength) lbs. is gradually added.

Theremainder of the arsenic and nearly all of the tin is extracted and passes unmixed with lead'oxide into the reagent, from which it maybe recovered. The temperature employed is 1100 to 420 C.

(c) The lead now contains no arsenic and is practically free from tin. It is finally treated for the removal of antimony by of a molten (98% NaOH) L64 lbs., sodium chloride (95% strength) .110 lbs., adding sodium nitrate (98% 182 lbs. gradually throughout the process. The temperature of the lead is about 420? C. All the antimony unmixed with lead passes into the reagent from which the former in its insoluble oxidized form may be separated from the solution as before and the reagents j recovered by evaporation. The-lead is now oxidizer.

in a particularly pure refined form. 'The yield will be practically 100 per cent of the original contents.

In all the above examples sodium chlorate may be substituted for sodium nitrate as an In use it has certain advantages The temperature compounds are soluble. To obtain the destrength) over the nitrate, its action being rather more easily controlled; but it is somewhat -more expensive and it does not give up alkali oxide in exchange as does sodium nitrate.

Hypochlorites and peroxides are also very 'eflicient preferential oxidizers when used in conjunction with caustic alkali or mixtures of caustic alkali and chlorids. 1 From the foregoing examples it will be understood by those skilled in the art to what extent the solid oxidizer can be added to the particular lead to be treated so as to obtain the valuable results according to my invention.

I might further point out that as regards the use of sodium chlorid with caustic soda as the molten reagent, the presence of the sodium chlorid in the caustic soda solution derived from dissolving the resulting melt produced by said process, as above pointed out, reduces the, solubility of the antimony compounds in said solution, so that if sufficient sodium chlorid is used in the molten reagent it will result in a substantially comabove pointed out, substantially all of the antimony compounds Will remain insoluble when this melt is dissolved in water, whereas 1n this resulting solution the tin and arsenic sired results in this regard, it is preferable to use suflicient sodium chlorid so that this resulting solution will contain sufiicient sodium chlorid to constitute it a saturated solution of the sodium chlorid, and to make sure of having the saturated solution it is preferable to use an actual excess of the sodium chlorid; but additional sodium chlorid may be added in solution formto the said resulting solution. The quantities set forth in theforegoing examples are such as to result in this excess. This use of the sodium. chlorid also helps mechanically in the separation of. the insoluble antimony compounds from said resulting solution, in

that the insoluble antimony compounds separate out in better physical form, that is to say, they gravitate or settle out of the solution more readily. The viscosity of the alkali hydroxid melt is increased by the'alkali chlorid, which is especially desirable for the separation therefrom of the arsenic,"

tin and-antimony, forms no part of the present invention, but is the subject matter of and is covered by my copending application Serial Number 676,261, filed November 22.

I 1923, for separation of ingredients from an tion -With particularity and by way of example in connection with the preferred method of carrying out the same, it will be understood by those skilled in the art, after understanding the invention, that various changes and modifications may be made without departing from the spirit or scope of the invention, and I aim in the appended claims to cover all such changes and modifi cations as come Within the scope of the invention. 1

What I claim is: I a

1. Process of refining lead which comprises bringing molten lead While maintained at a temperature not exceeding about 500 G. into intimate contact with a molten reagent comprising molten caustic alkali, and gradually adding an oxidizing agent in such limited quantity that substantially no lead oxide or alkali oxysalt of lead is found in the resulting melt.

2. Process of refining lead for the separation therefrom of one or more of the impurities arsenic, tin and antimony which comprises, circulating the molten lead while maintained at a temperature not exceeding about 500 C. and in distributed form, through a molten reagent comprising molten caustic alkali and gradually adding an oxidizer during the taking place of the reactions, the oxidizer being added at such a rate and in such quantity that substantially no lead oxide or alkali oxysalt of lead is found in theresulting melt.

3. Process of refining lead for the separation therefrom of one or more of-the impurities arsenic, tin and antimony which comprises circulating the molten lead while maintained at a temperature not exceeding about 500 C. and in distributed form, through a molten reagent comprising molten caustic alkali and sodium chlorid, and gradually adding an oxidizer during the tak- 1ng place of the reactions, the oxidizer being added at such a rate and in such quantity that" substantially no lead oxide or alkalioxysalt of lead is found in the resulting melt.

4. Process of refining lead which comprises bringing into intimate contact, molten lead while maintained at a temperature not exceeding about 500 (3., a reagent comprising caustic alkali and an oxidizin agent, the latter applied in such limited quantity and at such a rate that substantially nolead oxide or alkali oxysalt of lead is found in the resulting melt.

5. Process of refining lead which comprises bringing intointimate contact, molten lead while maintained at a temperature not exceeding about 500 0., a reagent comprising a caustlc alkali and an oxidizing agent, the latter applied at such a'rate and in such limited quantity that substantially no lead oxide or alkali oxysalt of lead is found in the melt at any period of the operation.

6. Process of refining lead which comprises bringing molten lead while maintained at a temperature not exceeding about 500 G. into intimate contact with a molten reagent comprising molte'n caustic alkali and a molten oxidizing agent, the latter used in such limited quantity that substantially no leadis permanently oxidized in the carrying out of the process.

7. Process of refining lead for the separation therefrom of one or more of the impurities arsenic, tin and antimony, which comprises bringing molten lead while main tained at a temperature not exceeding about 500-fl. into intimate contact with a molten reagent-,comprising molten caustic alkali, and a molten oxidizing agent gradually added to the caustic alkali in small quantities during the taking place of the reactions, the oxidizer being added at such a rate and in such quantity that substantially no lead oxide or alkalioxysalt of lead is found in the resulting melt.

8. Process of refining lead for the separation therefrom of one or more of the impurities arsenic, tin and'antimony, which comprises bringing molten lead while main tained at a temperature not exceeding about 500 G. into intimate contact with a molten mixture comprising a mixture of molten 10 caustic alkali and sodium chlorid and a molten oxidizing agent gradually added in small quantities during the taking place of the reactions, the oxidizing agent being added at such a rate and in such quantity that substantially no lead oxide or alkali oxysalt of lead is found in the resulting melt. 9. Process of refining lead for the separation of one or more of the impurities arsenic, tin and antimony, which comprises maintaining thelead at a temperature not exceeding about 500 C. and passing the molten lead in distributed form through a molten reagent mixture comprising caustic alkali and sodium chlorid and a suitable molten oxidizing agent such as those of the character herein set forth gradually added in small quantities during the taking place of the reactions, the quantity of the oxidizing agent being in approximately stoichiometric proportions to the impurity or impurities to be separated. I

10. The process of refining lead for the separation therefrom of one or more of the impurities arsenic, tin and antimony, which comprises bringing the molten lead while maintained'at a temperature not exceeding I about 500 G. into intimate contact with a molten mixture comprising a mixture of o t n. caustic s da and sodium ch rid to which an oxidizing agent is gradually added in such quantity that substantially no lead is permanently oxidized in the carrying out of the process, and in which molten mixture sodium chlorid is used in such quantity that the caustic soda solution derived from dissolving the resulting melt, contains suflicient sodium chlorid to render substantially all of the antimony compounds present insoluble therein, whereby they may be more readily separated from the soluble tin and or arsenic compounds.

11. The process of refining lead for the separation therefrom of one or more of the impurities arsenic, tin and antimony, whlch comprises bringing the molten lead while nlaintained' at a temperature not exceeding about 500 G. into intimate contact with a molten mixture comprising caustic soda and sodium chlorid and a molten oxidizing agent, the sodium chlorid being used in such quantity that in the caustic soda solution derived from diss'olvin the resulting melt sufiicient sodium chlorid will be present to constitute the solution a substantially saturated solution of sodium chlorid whereby substantially all of the antimony compounds present are rendered insoluble in said solution.

12.- Process of refining lead for the separation therefrom of one or more of the 1mpurities arsenic, tin and antimony which comprises circulating the molten lead while maintained at a temperature not exceeding about 500 C. and in distributed form, through a molten reagent comprising molten caustic alkali and a molten oxidizing agent gradually added to the caustic alkali in small quantities during the taking place of the reactions, the oxidizer being added at such a rate and in such quantity that substantially no lead oxide or alkali oxysalt of lead is found in the resulting melt.

13. The process of refining lead containing two. or more of the impurities arsenic, tin and antimony for fractional removal of said impurities in the order named, which comprises maintaining the molten lead at a temperature not exceeding about 500 C. and (if arsenic. is present) bringing the molten lead into intimate contact with a stantially an 6 ,molten reagent comprising molten caustic 7 tin is present and to be removed separate from antimony) bringing the thus treate l molten lead into intimate contact with a fresh batch of molten reagent comprisingmolten caustic alkali and gradually adding an oxidizing agent in limited quantity, the temperature of the molten lead and the amount and rate of addition of the oxidizer being such that most of the tin and the remaining amount of arsenic will be oxidized and found in the resulting melt without substantially any lead oxide or alkali oxysalt of out substantially any lead oxide or alkali oxysalt of vlead.

14. The process of refining lead containing two or more of the impurities arsenic, tin and antimony, for fractional removal of said impurities in the order named, which comprises maintaining the molten lead at a temperature not exceeding about 500 C;

and bringing the molten lead into intimate contact with separate batches of a molten reagent, one for each fractional-removal, the molten reagent comprising in each case molten causticalkali to which is gradually added during the reactions, anoxidizing agent in limited uantity, one or more of the batches of mo ten reagent also containing molten. sodium chlorid, and adjusting the temperature/of the molten lead and the amount and rate of addition of the oxidizing agent for the different fractional operations so as to facilitate the fractional removal of said impurities.

15. The process of refining lead containing two or more of the impurities arsenic, tin and antimony, for, fractional removal of said impurities in accordance with the process of claim 13, characterized by the fact that in one or more of the batches of molten reagent alkali chlorid is used with the molten caustic alkali.

16. Process of refining lead which comprises bringing into intimate contact, molten lead while maintained at a temperature not exceeding about 500 C. and a rea ent comprising caustic alkali, and gradually adding at a substantially uniform rate a solid 0x1- dizer during the taking place of the reactions.

'llntestimony whereof I have signed my name to this specification.

' ne e H R I 

